1. Technical Field
The invention relates to an apparatus for cooling chips on a circuit board.
2. Background Art
The demand for smaller, faster, more powerful computers and electronic devices has led to rapid technological advances in the development of smaller, more complex integrated circuits embedded in small pieces of semiconducting material, know as chips. In recent years, these advances have resulted in chips with increased operating speeds, more transistors, and enhanced performance. While these advances have led to smaller chips with faster circuits, they have also resulted in chips with increased power consumption and greater heat generation. As a result, heat dissipation requirements for chips have increased.
Additionally, the demand for smaller, more compact computers and electronic devices has led to more compact circuit board arrangements and smaller system housings. As a result, the space available for attaching heat dissipating devices and providing airflow over these devices has decreased. Due to increased dissipation requirements and airflow and space restrictions, there exists a need for more compact heat dissipating devices able to adequately cool chips while occupying minimal space.
FIG. 1 illustrates a commonly used heat dissipating device for chips, known as a conventional finned heat sink 1. This heat sink includes a base 2 and a plurality of fins 3 which extend from the base 2. The base 2 of the heat sink 1 is configured to attach to the top of a chip. Heat generated by the chip transfers through the base 2 of the heat sink to the fins 3 for ultimate dissipation to cooler surrounding air in the system. The fins 3 of the heat sink 1 are typically arranged so that airflow in the system will pass between the fins 3. In many systems, fans are used to increase airflow through the system, thereby accelerating the transfer of heat from the fins 3 to the surrounding air.
In more compact computer systems, space restrictions may not allow for placement of an adequately-sized conventional finned heat sink on top of a chip. In such cases, alternative heat dissipating devices must be considered. One alternative device, used more frequently in recent years, is a heat pipe.
Heat pipes typically include a sealed vessel with a vacuum formed inside. One end of a heat pipe (called the evaporator) attaches to the surface of a chip, and the other end of the heat pipe (called the condenser) extends away from the chip for exposure to cooler system air. Usually, heat pipes also include a wick structure inside the vessel, lining the walls of the vessel, and a working fluid inserted in the vessel, just enough to saturate the wick structure. The atmosphere in the vessel is set such that, absent heat transfer, the fluid is maintained at a liquid-vapor equilibrium.
When a heat pipe is attached to a chip generating heat, heat is transferred from the chip to the attached evaporator end of the heat pipe. This transfer of heat results in the generation of a higher pressure vapor at the evaporator end. The phase change of the fluid from liquid to vapor results in the absorption of a substantial amount of heat. The higher pressure of the vapor at the evaporator end of the heat pipe causes the vapor to flow in a direction toward the condenser end of the heat pipe. The lower temperature at the condenser causes the vapor to condense back to a liquid, thereby releasing its latent heat of vaporization to the condenser. The fluid condensed at the condenser end of the heat pipe then saturates the wick structure and gets pumped back to the evaporator end of the heat pipe by capillary forces developed in the wick structure. This continuous cycle of vaporization-condensation allows heat pipes to transfer large quantities of heat with very low thermal gradients. Heat pipes may also include a plurality of fins around the outside surface of the condenser to enhance heat dissipation from the condenser to the surrounding air, thereby, keeping the walls at the condenser cooler and increasing the heat transfer performance of the heat pipe.
In more compact computer systems where system components are placed closer together, space restrictions may not allow for the use of a conventional heat pipe which include an extending end surrounded by fins. Therefore, a more compact heat dissipation device able to adequately dissipate heat while occupying minimal space is desired. Additionally, in compact systems where two or more chips are placed in close proximity to each other, a compact heat dissipation device able to adequately dissipate heat from the two or more chips is desired.
One example of a circuit board configured for placement in a compact system is shown in FIG. 2. In this example, the circuit board 10 is the main board (or motherboard 10) of a computer system. This motherboard 10 includes an array of 8 chips (generally at 12) located between two connector banks where CPU models are to be connected to the motherboard 10 (connectors shown at 18). The motherboard board 10 mounts into a system such that two of the chips 14, 16 at the end of the array 12, which produce a great amount of heat, are located furthest from system fans (not shown). As a result, these chips 14, 16 receive the warmest air (after it has passes by other components in the system) and are the most difficult to keep cool. This cooling problem is further complicated by the fact that no room is available above one of the chips 16 for attaching a conventional finned heat sink. Additionally, no room is available around the chip for use of a conventional heat pipe with an extending end surrounded by fins. In view of these space restrictions and the general trend toward more compact systems and circuit boards and chips with greater heat dissipation needs, it can be seen that alternative heat dissipating devices which are compact in arrangement yet adequate in cooling are needed and increasingly desired.
In one aspect, the invention relates to an assembly for cooling chips. The assembly includes a heat sink, a plate member, and a heat pipe. The heat sink is attachable to a first chip. The plate member is attachable to a second chip. The heat pipe is arranged between the heat sink and plate member such that one end of the heat pipe attaches to the heat sink and another end of the heat pipe attaches to the plate member.
In another aspect, the invention relates to a chip cooling system for cooling chips. The chip cooling system includes a chip cooling assembly which attaches to a plurality of chips, and a airflow directing means for directing airflow across the chip cooling assembly. In one embodiment, the means for directing airflow includes an channel attached to the circuit board and extending over the chip cooling assembly and plurality of chips.
In another aspect, the invention provides a method for dissipating heat generated by a first chip and a second chip which are positioned near each other on a circuit board. The method includes transferring heat from the first chip to a heat sink by attaching the heat sink to the first chip. The heat sink includes a plurality of protruding members and a groove formed through the protruding members. The method also includes transferring heat from the second chip to a plate member by attaching the plate member to the second chip. The plate member has a groove formed in it. Additionally, the method includes transferring heat from the plate member to the heat sink by attaching a heat pipe to the heat sink and the plate member. The heat pipe has a first end and a second end. The first end is disposed within the groove of the heat sink. The second end is disposed within the groove of the plate member.
Advantages of the invention include, at least, a chip cooling assembly which can attach to multiple chips to provide cooling for the chips when space is not available proximal to one of the chips for attaching a conventional finned heat sink. Additionally, the invention may provide a cooling assembly which uses the fins of one heat sink to assist in the cooling of multiple chips.
Other aspects and advantages of the invention will be apparent from the following description and the appended claims.